1. Field of the Invention
The present invention relates to quinoxaline derivatives, and light-emitting elements, light-emitting devices, electronic devices which use the quinoxaline derivatives.
2. Description of the Related Art
Organic compounds can take more various structures compared with inorganic compounds, and have possibility to provide materials having various functions by appropriate molecular design. Owing to these advantages, photo electronics and electronics which utilize functional organic materials have been attracting attention in recent years.
For example, a solar cell, a light-emitting element, an organic transistor, and the like are exemplified as electronic devices utilizing an organic compound as a functional organic material. These devices utilize electric properties and optical properties of the organic compound. Among them, in particular, a light-emitting element has been making remarkable development.
It is said that light emission mechanism of a light-emitting element is as follows: when a voltage is applied between a pair of electrodes with a light-emitting layer interposed therebetween, electrons injected from a cathode and holes injected from an anode are recombined in the light emission center of the light-emitting layer to form a molecular exciton, and energy is released to emit light when the molecular exciton makes the transition to a ground state. As excited states, a singlet excited state and a triplet excited state are known, and light emission is considered to be obtained from any of these excited states.
Such a light-emitting element has a lot of problems which depend on materials, in improving the element characteristics. In order to solve these problems, improvement of an element structure, development of a material, and the like have been carried out.
For example, WO 2004/094389 (Reference 1) discloses that a quinoxaline derivative is used for a light-emitting element.